More than 90% of the HIV infections in the world are in developing countries and 80% are in sub-Saharan Africa. Seroprevalence in east,c central, and southern African urban adults ranges from 10 to 30%. In the USA, sexual and vertical HIV transmission have been greatly reduced due to successful prevention campaigns and aggressive perinatal anti-retroviral therapy. Clinical trials of new prevention interventions will require large sample sizes that are no longer accessible or affordable domestically. Simultaneously, it is becoming evident that a clear understanding of the determinants of transmission requires study of virus and host in geographically disparate areas with different subtypes of HIV and different host genetic characteristics and immune responses. The UAB-CFAR International Research Core proposes to act as a liaison between the multi-disciplinary teams team of HIV/AIDS researchers at UAB and investigators at field sites with unique high risk groups and patient populations. The focus will be Zambia , where three NIH grants and a contract are in place and additional proposal is pending. The ongoing Zambia studies include epidemiologic, virologic, immunologic, and immunogenetic studies of heterosexual transmission in discordant married couples, where a cohort of 700 discordant couples-the largest single site cohort of its kind in the world-has been enrolled. Strong collaborative links have been established with the University Teaching Hospital, Tropical Disease Research Centre, and Ministry of Health National AIDS Control Programme in Zambia and thirteen Zambian physicians, nurses, and laboratory technicians have received specialized training at UAB. The International Research Core proposes to provide liaison and support services to facilitate UAB-Zambia collaborative studies. These include practical assistance with development of collaborative projects (organization of formal and informal conferences and meetings between UAB and Zambia-based researchers; facilitation of IRB clearance and approvals from relevant authorities in Zambia and at UAB); procurement, processing, storing, and shipping of samples; and logistics of communications (e-mail. telephone, fax, word processing and scanning services in Zambia) and travel (coordination of visits by UAB researchers to Zambia and vice-versa to ensure complementarity; hosing and transport). Charge back systems will be implemented with existing and future grants to recover on site costs.